This invention relates generally to printers, and more particularly to media ejection systems for stacking media sheets in an output region or output tray.
Print jobs commonly include multiple media sheets fed along a media handling system through a print zone into an output tray or output region. Media sheets are fed in series with one sheet along the media path at a time for some printers or with multiple sheets along the media path at a time for other printers. Media sheets are stacked in the output tray. Many printers, especially ink jet printers, use a star wheel drive and an output roller to propel media sheets as the media sheets exit the media path. Ejected by the star wheel, the media sheet glides down the output roller by its own gravity and the momentum it gained during the ejection. In the conventional ejection mechanism of star wheel drive and output roller, however, the maximum momentum gained by the media sheet during the ejection is limited by the print swath width. And the ink contents make the media sheet sag and touch the previously printed media. This action resists the movement of the sheet. As a result, the media sheet has a tendency to cling to the surface of the output roller nearer to the star wheel interface, especially if the surface is rubber. Therefore, when it comes, the next media sheet hits the one clinging to the output roller. xe2x80x9cBull dozingxe2x80x9d effect takes place and output stack gets disturbed.
U.S. Pat. No. 5,890,821, issued Apr. 6, 1999 for xe2x80x9cPrint Media Ejection Kicking after Paper Dropxe2x80x9d assigned to Hewlett-Packard Company, discloses movable pivot devices used during ejection. The ejection system includes a movable pivot which supports the media sheet within the printing zone during printing. Upon completion of the printing, the pivot moves downward allowing the current media sheet to slide from the pivot into the output tray. This patent also introduces a kicker device coupled to the output tray to drive any remaining portion of the media sheet into the output tray. Nevertheless, coordinating the movement of the kicker device and pivot adds complexity to the ejection design.
In a preferred embodiment, the present invention provides a simplified structured print media ejection system that actively pushes a media sheet forward.
An embodiment of a print media ejection system according to the invention includes an output roller. A plurality of protrusions is selectively positioned on the roller. As the media sheet exits the media path, the rear edge of the media sheet is caught and further pushed forward into an output stack by the protrusions. The roller thus enhances the momentum of the ejected media sheet by propelling its rear edge and consequently reduces the possibility of xe2x80x9cbull dozingxe2x80x9d.
Besides, the output roller also includes at least one longitudinal section without said protrusions.
Preferably, to catch the rear edge of the media sheet, the distance between the end edge of the protrusions and the axis of the roller is slightly longer than the radius of non-protrusion parts of the roller. Nevertheless, the preceding distance is limited so that the protrusions will not disturb the movement of the media sheet.
It is also preferred that the protrusions are located at certain parts of the roller, e.g., the middle part and/or the end part.
According to one aspect of the invention, the protrusions are flexible. Preferably, they are made of flexible materials, such as molded rubber. Besides, the protrusions are biased in a direction for the media sheet to be pushed. It is also preferred that the protrusions extend radially slightly above the non-protrusion parts of the output roller.